Hydrogenolysis/isomerization process

ABSTRACT

A process for selective hydrodealkylation of ethylbenzene in a hydrocarbon feedstock comprising ethylbenzene and xylenes, and for simultaneous isomerization of the xylenes, which comprises contacting the feedstock with a catalyst comprising a cobalt or nickel component on an acidic inorganic refractory oxide support at a temperature between 650*-950*F., a pressure below 300 psig, and a hydrogen-to-hydrocarbon feed ratio between 1:1 and 20:1. Preferably the catalyst used is cobalt on silica-alumina.

United States Patent Ransley HYDROGENOLYSlS/ISOMERIZATION PROCESS [75]Inventor: Derek L. Ransley, Berkeley. Calif.

[73] Assignee: Chevron Research Company, San Francisco, Calif.

[22} Filed: Mar. 18, 1974 [21] Appl. No.: 452,489

[52] US. Cl 260/672 R; 260/668 A; 260/672 T [51] Int. Cl. C07c 3/58 [58]Field of Search 260/672 R. 672 T. 668 A [56] References Cited UNITEDSTATES PATENTS 2.564.388 8/l95l Bennett et al. 260/668 3.088.984 5/1963Oldenburg 260/668 3.548.0l7 l2/l970 Hebert et al 260/668 [45] Nov. 11,1975 Primary Examiner-Delbert E. Gantz Assistant Examiner-C. E. SpresserAttorney. Agent. or Fz'rmG. F. Magdeburger; John Stoner. Jrr. T. G. DeJonghe [5 7] ABSTRACT A process for selective hydrodealkylation ofethylbenzene in a hydrocarbon feedstock comprising ethylbenzene andxylenes. and for simultaneous isomerization of the xylenes. whichcomprises contacting the feedstock with a catalyst comprising a cobaltor nickel component on an acidic inorganic refractory oxide support at:1 temperature between 650-950F.. a pressure below 300 psig. and ahydrogen-to-hydrocarbon feed ratio between lzl and 20:1. Preferably thecatalyst used is cobalt on silicaalumina.

3 Claims. 1 Drawing Figure Co AROMATlCS Ca AROMATICS HYDRODEALKYLATTON-lSOMERlZATION ZONE RECYCLE AROMATICS & ALKANES US Patent Nov. 11, 19753,919,339

Ca AROMAT'ICS 8 & ALKANES AROMATICS P-XYLENE N SEPARATION YLE E ZONE I 2BLEED Ca AROMATICS HYDRODEALKYLATION- ISOMERIZATION ZONE .2 F RECYCLEAROMATICS 8. ALKANES HYDROGENOLYSlS/ISOMERIZATION PROCESS BACKGROUND OFTHE INVENTION The present invention relates to concurrenthydrodealkylation and isomerization of alkyl aromatics, preferablyhydrodealkylation of ethylbenzene with simultaneous isomerization ofxylenes.

Hydrodealkylation of alkyl aromatics has been known for some time. Forexample, U.S. Pat. No. 2,422,673 discloses hydrodealkylation ordemethylation of an alkyl aromatic using a catalyst containing nickel orcobalt on diatomaceous earth. Temperatures used in the process of U.S.Pat. No. 2,422,763 are between 350-650F. and pressures are betweensubatmospheric to 1,000 psig. According to the patent, it is generallyadvisable to carry out the reaction at a fairly low pressure of hydrogenso as to obtain a relatively high proportion of demethylation and arelatively small amount of hydrogenation of aromatic hydrocarbons tonaphthenic hydrocarbons.

U.S. Pat. No. 2,734,929 also discloses hydrodealkylation of alkylaromatics, including a process for removing ring-bonded methyl groupsfrom the aromatic ring, which methyl groups are more difficult to removethan splitting a longer-chained alkyl group down to a shorterside-chained group. According to the patent, the catalyst used containsa Group Vl-B or Group Vlll metal hydrogenation component, such aschromium, molybdenum, tungsten, uranium, iron, cobalt, ruthenium,rhodium, palladium, osmium, iridium or platinum, platinum being theleast preferred. The hydrogenation catalyst is preferably suspended on acarrier such as alumina, silica gel, zirconia, thoria, magnesia,titania, montmorillonite clay, bauxite, diatomaceous earth or crushedporcelain. The alumina carrier can also contain some silica. The U.S.Pat. No. 2,734,929 patent discloses preferred operating conditionsincluding a pressure between 150-200 psig and a temperature between900-1200F.

U.S. Pat. No. 3,478,120 discloses a process for hydrodealkylation ofethylbenzene to toluene, benzene, methane and ethane, with thehydrodealkylation being carried out in the presence of xylenes. Thecatalyst used in the process of U.S. Pat. No. 3,478,120 comprises aniron-group metal on calcium aluminate. Operating conditions include areaction temperature of about 700F. and a pressure of about 200 psig.

lsomerization of alkyl aromatics is disclosed in numerous references.For example, U.S. Pat. No. 2,403,757 is an early patent disclosing theuse ofa synthetic silica-alumina catalyst for xylene isomerization at atemperature between 500l 100F. The use of hydrogen or steam in theisomerization of alkyl aromatics is disclosed in U.S. Pat. Nos.2,564,388, 2,775,628 and subsequent references.

Catalysts with Group Vl-B or Group VIII metals supported on a carrierhave also been disclosed for hydroisomerization. For example, U.S. Pat.No. 3,113,979 discloses use of a catalyst containing a Group VIII metalsuch as platinum, as well as boria, on a support such as alumina. U.S.Pat. No. 3,538,174 discloses platinum and iridium on a porous inorganicoxide support as an alkyl-aromatic hydroisomerization catalyst, and alsomentions that catalysts such as nickel sulfide on silica-alumina havebeen proposed as xylene isomerization catalysts. U.S. Pat. No. 3,562,342discloses hydroisomerization using a catalyst containing nickel and 2tungsten on a cracking component composed of a inixture of amorphousinorganic oxides and a synthetic crystalline zeolite in hydrogen form.U.S. Pat. No. 3,119,886 discloses hydroisomerization of xylenes using acatalyst containing nickel and tungsten on a synthetic aluminosilicatesupport.

lsomerization and disproportionation of alkyl aromatics is disclosed inU.S. Pat. Nos. 3,651,162 and 3,578,723. According to U.S. Pat. No.3,651,162, alkyl aromatic hydrocarbons are isomerized anddisproportionated by contacting them at elevated temperatures in thepresence of hydrogen gas with a catalyst comprising a silica-aluminacracking base impregnated with a hydrogenation component, a second metalfrom Group V-A of the periodic table, and a halogen. The preferredhydrogenation component is nickel, the preferred Group V-A metal isarsenic, and the preferred halogen is fluorine. Example I of U.S. Pat.-No. 3,651,162 discloses conversion of metaxylene to other xylenes,toluene, trimethylbenzene and benzene at a temperature preferablybetween 700900F.

U.S. Pat. No. 3,578,723 describes the use ofa zeolite catalyst forconversion of mixtures such as toluene and trimethylbenzene to xylenesor converting orthoxylene to triand tetramethylbenzenes such as durene.

SUMMARY OF THE INVENTION According to the present invention, a processis provided for selectively hydrodealkylating ethylbenzene in ahydrocarbon feedstock comprising ethylbenzene and xylenes, and forsimultaneously isomerizing the xylenes, which process comprisescontacting the feedstock with a catalyst comprising a cobalt or nickelcomponent on an acidic inorganic refractory oxide support at atemperature between 650-950F., a pressure below 300 psig and ahydrogen-to-hydrocarbon feed ratio between 1:1 and 20:1.

1 have found that cobalt on silica-alumina is an especially preferredcatalyst for use in the process of the present invention.

The cobalt or nickel catalyst components can be present in compound formsuch as the oxides or sulfides or in elemental form or partly incompound form and partly in elemental form. Preferably the metal ispresent in the catalyst in a reduced state. Preferably the catalyst isobtained by impregnating a cobalt salt into the support, calcining, andthen heating in a hydrogen atmosphere, which results in conversion of asubstantial portion of the metal salt into the elemental form.Furthermore, in the presence of hydrogen, as used in the process of thepresent invention, the cobalt or nickel remains essentially in theelemental form.

Among other factors, the present invention is based on my finding that ahigh degree of selective hydrodealkylation of ethylbenzene to tolueneand benzene can be obtained in the presence of xylenes whilesimultaneously isomerizing the xylenes, when using a catalyst comprisingcobalt or nickel on an acidic inorganic refractory oxide support.

The term "acidic" inorganic refractory oxide support is used herein toconnote acid-acting solid supports such as silica-alumina or inorganicrefractory oxides such as alumina containing about 0.3 to 5 weightpercent halide, namely chloride, bromide or fluoride. Usually a purealumina support is not sufficiently acidic for purposes of the presentinvention.

The cobalt or nickel component of the catalyst may be referred to as ahydrogenation component. In accordance with a preferred embodiment ofthe present invention, the hydrogenation component is cobalt. l havefound that a particularly preferred catalyst for use in the process ofthe present invention comprises a cobalt component on silica-alumina.

Among other factors, this particularly preferred embodiment is based onmy unexpected finding that cobalt on silica-alumina is considerablysuperior to nickel on silica-alumina in terms of the beneficial resultsachieved in the process of the present invention. including a higherselectivity for ethylbenzene conversion in the presence of xylenes andlower disproportionation losses, than is achieved using thecorresponding nickel-containing catalyst.

Preferred operating conditions for use in the present invention includea temperature between 700-900"F. and a hydrogen pressure between l-200psig. Particularly preferred operating conditions. especially when usingthe cobalt-on-silica-alumina catalyst, include a temperature between750850F. and a pressure between l0200 psig. These preferred operatingtemperatures and pressures are especially important in achieving thesimultaneous selective hydrodealkylation of ethylbenzene andisomerization of xylenes.

Preferred hydrogen-to-hydrocarbon ratios for the feed to the process ofthe present invention are between about 1 to 20, and more preferredratios are between about 5 to l0.

Preferred space velocities for the hydrocarbon feed to the catalyticreaction zone of the present invention are between about 0.1 to LHSV(liquid hourly space velocity), and more preferably between about 0.3and 1.0 LHSV.

The present invention has been found to be especially advantageouslyapplied to feedstocks containing a relatively large amount of xylenes,that is, at least 50 weight percent xylenes, and more preferably atleast 60 or even as high as 70 or 80 weight percent xylenes. Even thoughthere are large amounts of xylenes presem. a selective hydrodealkylationof ethylbenzene has still been found to be achieved when using theprocess of the present invention. The amount of ethylbenzene in the feedto the present invention is usually between 5 to 40 weight percent, andpreferred feedstocks include those having between 10 to 30 weightpercent ethylbenzene. With the process of the present invention inoperation and with recycle through a paraxylene plant, the ethylbenzeneconcentration levels out at about 10%.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flowdiagram illustrating a preferred embodiment of the present invention.

FURTHER DESCRIPTION AND EXAMPLES The process of the present invention isuseful in refinery operations wherein a C aromatics stream is processedto recover the maximum amount of paraxylene. The paraxylene-reducedeffluent from a paraxylene plant is a particularly preferred feedstockin the process of the present invention. Concurrent hydrodealkylationand isomerization prevents the buildup of large quantities ofethylbenzene in the recycle stream, and at the same time convertsorthoand met-axylenes into the more desirable paraxylene. A typicalcyclic process utilizing the process of the present invention is shownin the drawing.

As indicated in the drawing, a mixed aromatic feed in line I, previouslytreated to remove nonaromatic components, is combined with the line 2effluent stream from hydrodealkylation/isomerization plant 15, fed vialine 3 to column 4, and distilled. The higher-boiling aromatics thosehaving more than 8 carbon atoms are taken as a bottoms fraction in line5; the overhead is charged via line 6 to another distillation unit, 7.In this second distillation, the lower-boiling aromatics those havingless than 8 carbon atoms and the alkanes. methane and ethane are takenoverhead in line 8. The bottoms from the second distillation are thenfed via line 9 to paraxylene plant 10, wherein about 25 to 95 percent ofthe paraxylene is removed by crystallization or by extraction, andparaxylene is withdrawn via line ll. The effluent (mother liquor) fromthe paraxylene plant then is withdrawn via line 12 and is fed to theconcurrent hydrodealkylation/isomerization plant 15. Provision is madevia line 13 to bleed some of the paraxylene plant mother liquor asdesired. Finally, the ethylbenzene-reduced/xylene-isomerized stream fromthe hydrodealkylation/isomerization plant is recycled to be combinedwith incoming fresh feed.

Typical fresh feed to such a combined process contains about l5 to 30percent ethylbenzene based on C aromatics. The recycle stream containsabout 5 to l5 percent ethylbenzene based on C aromatics. Finally, whenoperating this above-described combined process in a continuous manner,the quantity of recycle C aromatics is from two to four times that ofthe fresh feed; and, as a consequence, the ethylbenzene in the feed tothe paraxylene plant levels out at less than 10 percent, as compared toabout 20 percent on a once-through or single-pass basis. Such areduction in ethylbenzene concentration increases the efficiency of theparaxylene plant, especially one using crystallization-type separation.

The catalysts used in the process of the present invention arepreferably prepared by mixing the desired solid support with an aqueoussolution of a cobalt or nickel salt. The resulting slurry can beevaporated to dryness. or the solution-covered solid support can befiltered from the slurry and dried. in the first method, the slurry mustbe stirred during evaporation to ensure even coverage. In the secondmethod. this is not necessary. [n the first method of catalystpreparation, the quantity of metal on the catalyst support is easilycontrolled.

Cobalt and nickel salts useful in the formation of aqueous solutions forcatalyst preparation include the nitrates, acetates and sulfates. Thenitrates are preferred.

EXAMPLE 1 Preparation of a cobalt catalyst A solution of 5.0 g of cobaltnitrate in sufficient water to give 32 ml was added to 95 g of a /10silica/alumina support. The solid material was blotted dry after 15minutes of immersion. It was then dried in an oven at 250F. for 16hours. A portion of this dried material 27.25 ml was charged to ainch-diameter stainless-steel tubular reactor. It was then heated at900F. in air for one hour at atmospheric pressure and then at 900F. in ahydrogen atmosphere for one hour at I00 psig. The resulting catalystcontained 1.3 percent by weight of cobalt.

EXAMPLE 2 Preparation of a nickel catalyst The procedure of Example 1was followed, except that the impregnating solution contained 12.3 g ofnickelous nitrate in sufficient water to give 35.2 ml. The resultingcatalyst contained 2.4 percent nickel.

E XA M P LES 3-8 Other catalysts Other catalysts were prepared in asimilar way to give a range of metal concentrations and to give avariety of supports. These were as follows:

Percent Hydrodealkylation/lsomerization (a) A stainless-steel, vertical,tubular reactor, having an ID of A inch and mounted in an electricallyheated metal block, was charged with the catalyst of Example 5. Thereactor was heated to 800F., and the pressure was adjusted to 75 psig.Then hydrogen and a C aromatic hydrocarbon in a molar ratio of 7.6:1 wasfed to the reactor at an LHSV of 0.88 hr". The aromatic hydrocarboncontained 23% ethylbenzene, 8.1% paraxylene, and 66.5% other xylenes.After 16 hours on stream, the effluent hydrocarbon was analyzed by massspectra and vapor-phase chromatography and found to contain thefollowing components (in weight percent): 0.7% nonaromatics, 0.7%benzene, 12.2% toluene, 11.5% ethylbenzene, l4.4% paraxylene, 38.7%metaxylene, l9.7% orthoxylene, and 2.2% C aromatics. Thus, the reactionhydrodealkylated 50 percent of the ethylbenzene (l 1.5/23 X 100) andconcurrently isomerized the xylenes to increase the quantity ofparaxylene with only a 2.4 percent loss in total xylenes. Theisomerization level of the product was 84.9 percent, compared to 46.8percent for the feedstock. lsomerization level (IL) refers to thepercent approach to xylene equilibrium, and is calculated by thefollowing formula:

[L Weight total xylenes For commercially useful processes, the [L shouldbe over 80 percent, preferably in the range 90 to 100 percent.

b. The temperature was then raised to 875F., and the run was continuedfor 8 more hours. At the end of this time, the product stream had an [Lof 92.2 percent, and 71.3 percent of the ethylbenzene in the feed wasremoved by hydrodealkylation with only an 8.6 percent loss of totalxylenes. The ratio of ethylbenzene loss to xylene loss is 8.3(7l.3/8.6).

This example shows that concurrent hydrodealkylation and xyleneisomerization take place over the catalyst of this invention and thatthe levels of both are increased by increasing the temperature.Furthermore, it shows that these beneficial results are obtained withoutan uneconomical loss of xylenes.

EXAMPLE 10 No metal on the support The reactor of Example 9 was chargedwith the catalyst of Example 8. Hydrogen and an aromatic feed having21.5% ethylbenzene, 10.1% paraxylene and 68.4% other xylenes were fed tothis reactor at an LHSV of 0.44 hr". The mo] ratio ofhydrogen/hydrocarbon was 5.011. The reactor was maintained at atemperature of 800F. and a pressure of 50 psig. Under these conditions,the product stream had an isomerization level of 98.1 percent, but thehydrodealkylation of ethylbenzene was very low about 15 percent. Xyleneloss was 9.2 percent.

This example illustrates that the silica/alumina support without metaleffects isomerization but is a poor hydrodealkylation catalyst and isessentially nonselective in hydrodealkylation; the ethylbenzeneloss/xylene loss ratio was only 1.5.

EXAMPLE 1 l Cobalt on an alumina support & on a silica support a. Thecatalyst of Example 3 was charged to the same reactor as in the previousexamples and was then heated to 825F. Hydrogen and an aromatic feedhaving 26.3% ethylbenzene, 9.4% paraxylene, and 59.5% other xylenes werecharged at an LHSV of 2.4 hr. The hydrogen/aromatic hydrocarbon mo]ratio was 4.8:1. The pressure was 215 psig. The product stream had an lLof 58.6 percent. Ethylbenzene loss by hydrodealkylation was 60.9percent, and xylene loss was 21.5 percent.

b. The same run was carried out over the catalyst of Example 4, exceptthat the pressure was 205 psig and the temperature was 775F. In thiscase, the product had an [L of 56.9 percent and an ethylbenzenehydrodealkylation loss of 56.3 percent. The xylene loss was 10.5percent.

The two runs of this example illustrate that the metal portion of thecatalyst on either an alumina or a silica support alone effectshydrodealkylation of ethylbenzene without any isomerization of xylenes(1L of feedstock 58.5 percent).

EXAMPLE 12 Comparison of cobalt and nickel catalysts a. The catalyst ofExample 1 was charged to the reactor and heated to 800F. under apressure of 100 psig. Then hydrogen and an aromatic hydrocarbon in amolar ratio of 10.4:1 was fed at an LHSV of 0.73 hr. The aromatic feedcontained 9.7% ethylbenzene, 9.9% paraxylene, and 80.4% other xylenes.The product had an lL of 94.4 percent. The hydrodealkylation ofethylbenzene was 16.6 percent, and the xylene loss was 5.7%.

b. The catalyst of Example 2 was then charged and heated to 800F. undera pressure of psig. Hydrogen and an aromatic hydrocarbon in a molarratio of 4.911 were fed at 0.73 hr. This aromatic feed contained 8.5%ethylbenzene, 9.2% paraxylene, and 91.3 percent other xylenes. Theproduct from this reaction had a 94.8% 1L, and the hydrodealkylation ofethylbenzene was 76.5 percent. However. the hydrodealkylation loss ofxylenes was 28.5 percent.

These two runs illustrate the superiority of cobalt over nickel as themetallic portion of the catalysts used in the process of the presentinvention. Both metals effect about the same level of isomerization, butunder conditions that give a nickel catalyst this degree of activity.too much xylene is lost to hydrodealkylation. Lowering the temperaturein run 12(b) to 750F. did lower the xylene loss to 20.3 percent, but atthe same time the IL dropped to 87.9 percent. At the commerciallyfeasible percent or less xylene hydrodealkyla tion loss, the IL is wellbelow the feasible level.

c. Another run was carried out using the nickel catalyst of Example 7under similar conditions i.e.. 800F., 80 psig. 0.73 hr LHSV, and a 4.9:]ratio of reactants. The IL was 98.3 percent, but at the same time 22.8percent of the xylenes were lost.

d. Another run was carried out using the cobalt catalyst of Example Iunder more strenuous conditions than in any of Example 12(a), (b) or (c)i.e., 900F., 83 psig, 0.44 hr LHSV, and a molar ratio of reactants of3.4:1. In this case. the IL was 97.2 percent, but the loss of xyleneswas only 6.3 percent, and hydrodealkylation removed 19.7 percent of theethylbenzene.

This last run illustrates the specificity and superiority of the cobaltcatalyst to effect a high degree of isomerization without acorrespondingly high loss of xylenes to other aromatic by-products.

EXAMPLE 13 A low-pressure reaction The catalyst of Example 4 was chargedto the reactor and heated to 800F. under 14 psig. Then hydrogen and anaromatic feedstock in a molar ratio'of 4.9:! was fed at an LHSV of 0.37hr. The aromatic feed contained 9.2 percent ethylbenzene. 10.7 percentparaxylene, and 80.1 percent other xylenes. The product had an IL of97.5 percent. Hydrodealkylation of ethylbenzene was 34.5 percent, andloss of xylene was 8.9 percent.

What is claimed is:

l. A process for selective hydrodealkylation of ethylbenzene in ahydrocarbon feedstock comprising ethylbenzene and xylenes. to therebyconvert ethylbenzene to toluene and benzene, and for simultaneousisomerization of the xylenes. which comprises contacting the feedstockwith a catalyst consisting essentially of a cobalt component on asilica-alumina support at a temperature between 650 and 950F., apressure below 300 psig. and a hydrogen-to-hydrocarbon feed ratio between l:l and 20:l.

2. A process in accordance with claim 1 wherein the temperature isbetween 700-900F. and the pressure is between 10 psig and 200 psig.

3. A process in accordance with claim 1 wherein the temperature isbetween 750900F. and the pressure between l0 psig and 200 psig.

1. A PROCESS FOR SELECTIVE HYDRODEALKYLATION OF ETHYLBENZENE IN AHYDROCARBON FEEDSTOCK COMPRISING ETHYLBENZENE AND XYLENES, TO THEREBYCONVERT ETHYLBENZENE TO TOLUENE AND BENZENE, AND FOR SIMULTANEOUSISOMERIZATION OF THE EXYLENES, WHICH COMPRISES CONTACTING THE FEEDSTOCKWITH A CATALYST CONSISTING ESSENTIALLY OF A COBALT COMPONENT ON ASILICA-ALUMINA SUPPORT AT A TEMPERATURE BETWEEN 650* AND 950*F, APRESSURE BELOW 300 PSIG AND A HYDROGEN-TO-HYDROCARBON FEED RATIO BETWEEN1:1 AND 20:1.
 2. A process in accordance with claim 1 wherein thetemperature is between 700*-900*F. and the pressure is between 10 psigand 200 psig.
 3. A process in accordance with claim 1 wherein thetemperature is between 750*-900*F. and the pressure between 10 psig and200 psig.